1. Field of the Invention
The present invention relates to an apparatus for passively producing at least two distinct signal patterns for use, for example, in an identification of friend or foe (IFF) system to determine the friendly or unfriendly status of a potential target, adversary, or entity.
2. Background of Invention
Apparatus are known for producing distinct signal patterns. For example, in military applications, it is often desired to make an IFF determination, so that command authority can take an appropriate response. For commercial applications, an IFF can be used to identify objects with which it is desired to establish communications or otherwise interact. In addition to locating an object, the IFF""s ability to discriminate between friendly and unfriendly units can help manage and coordinate their deployment in a theater of operations.
Such a device should be able to identify objects quickly and reliably over a broad frequency range. It is useful to perform this identification process in a passive mode, so that no active radiation or energy is generated and emitted that can betray the device or its position to any undesired entity.
There are various types of known IFF systems. Many of these systems use an active transmitter to transmit a coded signal query to a receiver unit. The receiver analyzes the coded signal query and, upon successful decoding and acknowledgment of the signal, an identifying coded response is sent back. The operational scenario behind this process is that only friendly objects can intelligibly recognize, decode and properly respond to these transmitted queries. If after a certain response time no reply to the query is forthcoming, the entity is presumed hostile and appropriate action can be taken.
For example, U.S. Pat. No. 5,355,241 discloses a retroreflector that operates at optical wavelengths and uses an active source for establishing a transmitting and receiving communication path to interrogate the system for data extraction. U.S. Pat. No. 5,539,565 discloses an optical retroreflector which operates in the visible wavelength spectrum and uses an interrogation and acknowledgment signaling process to respond with a transmitted code upon receiving an interrogation inquiry. The disclosures of these patents are hereby incorporated by reference in their entireties.
The present invention is directed to a system for passively producing at least two distinct signal patterns. The system can be used for passively identifying friend or foe in an environment and operates in a hyper spectral mode that accommodates multiple bands simultaneously. Exemplary embodiments receive radiated energy within a resonant cavity, and use an absorber and a reflector to absorb and reflect desired frequencies of the incoming energy. A controller is connected to the IFF system and controls the switching back and forth between the absorber and the reflector to produce a signal having a desired data format. The encoded data can be used to determine the status of the candidate target.
Exemplary embodiments comprise a resonant cavity having an aperture for receiving radiated energy; an absorber and a reflector contained within the resonant cavity for receiving the radiated energy; and a controller to control switching of the absorber and the reflector to produce an identification signal data format. In exemplary embodiments, the signal patterns can be visible at multiple bands (e.g., radio frequency (RF), infrared (IR) and visible) simultaneously (i.e., hyper spectral). The aperture couples the resonant cavity to free space. The resonant cavity can be a waveguide for transmitting an incoming interrogating frequency. The aperture couples the waveguide to free space and also couples the resonant cavity to a lens assembly. The aperture couples the waveguide to a lens assembly.
The present invention utilizes radiated energy that is within at least one of radio, infrared and visible frequency spectrums. In exemplary embodiments, the distance between the aperture and the reflector is at least one half the wavelength of a lowest frequency of operation. The reflector can comprise a mirror, a prism, a diffraction grating or a Micro Electro Mechanical System (MEMS). A hermetically sealed container is used to house the resonant cavity, the absorber and reflector, and the controller.